Electric products, such as air cleaners and air conditioners, are equipped with an electrostatic precipitator to charge suspended particles by using a discharge.
The electrostatic precipitator includes a charger charging suspended particles by discharging and a dust collector collecting charged suspended particles. As for the charger of the electrostatic precipitator, a high voltage of several kV is applied to generate a discharge between a high voltage (discharge) electrode and a counter (ground) electrode.
When a discharge current flowing between the high voltage electrode and the counter electrode becomes large to obtain the high dust-collection efficiency, ozone (O3) may be easily generated according to the discharge. The ozone (O3) has unique smell and thus when the ozone (O3) is discharged to the indoor, it is needed that the ozone level is below the environmental standard (0.05 ppm).
Patent document 1 discloses a precipitator provided with an ion emitter emitting an ion without performing the corona discharge; and a dust collector formed in the downstream side thereof. The precipitator is configured such that a discharge electrode of the ion emitter is provided as a single or a plurality of linear electrodes and a ground electrode is formed on opposite sides of the linear electrodes, and an electrode connected to the ground is covered with an insulator or a semiconductor so that a discharge current is 1 μA or less than 1 μA a per 0.1 m linear electrode when a high voltage is applied to the linear electrode.
Patent document 2 discloses an electric dust collecting unit provided with an intake grill having a discharge needle to allow the high voltage to be applied thereto and having the center thereof expended to the front side, and a filter unit configured to ventilate, disposed in the downwind side of the discharge needle and to which a ground electron and a dust collecting filter are installed. The intake grill is formed such that non-conductive ribs formed of non-conductive resin and conductive ribs formed of conductive resin are arranged in a grid pattern and the conductive rib is connected to the ground electrode. Accordingly, the static electricity charged to the intake grill is discharged and thus dust is prevented from being attached to the intake grill.
Patent document 3 discloses a corona discharge device provided with a plurality of discharge members, a resistor connected to each of the discharge member, and a voltage source connected to the resistor.
Patent document 4 discloses an ion generator provided with a high voltage generator generating a high voltage and an ion generator having an ion generating electrode connected to an output of the high voltage generator to generate ions. The ion generator has an ozone generating electrode connected in parallel with the ion generating electrode in the output of the high voltage generator, and an impedance varying device connected in series with the ion generating electrode, and thus the ion generator is capable of controlling the amount of ozone generated in the ion generating electrode by changing the impedance of the impedance varying device.
Non-patent document 1 discloses that one side of an electrode is covered with a high resistance sheet of a few MO/cm instead of a dielectric. It is disclosed that a discharge occurs in a pulse shape that can be repeated with several 10 kHz in a width of a few μs, when operated by the direct current (DC).